The present invention relates to zinc free insulin crystals having a diameter below 10 xcexcm and to therapeutic powder formulations suitable for pulmonary administration comprising such insulin crystals.
Diabetes is a general term for disorders in man having excessive urine excretion as in diabetes mellitus and diabetes insipidus. Diabetes mellitus is a metabolic disorder in which the ability to utilize glucose is more or less completely lost. About 2% of all people suffer from diabetes.
Since the introduction of insulin in the 1920""s, continuous strides have been made to improve the treatment of diabetes mellitus. To help avoid extreme glycaemia levels, diabetic patients often practice multiple injection therapy, whereby insulin is administered with each meal.
Insulin is usually administrated by s.c. or i.m. injections. However, due to the adherent discomfort of injections alternative ways of administration such as nasal and pulmonary has been extensively investigated. For a review on alternative routes of administration of insulin, see Danielsen et al. New routes and means of insulin delivery, in: Childhood and Adolescent Diabetes (Ed. Kelnar), Chapman and Hall Medical, London 1994, pp. 571-584.
In order to circumvent injections, administration of insulin via the pulmonary route could be an alternative way to provide absorption profiles which mimic the endogenous insulin without the need to inject the insulin.
Administration of insulin via the pulmonary route can be accomplished by either an aqueous solution or a powder preparation. A description of the details can be found in several references, one of the latest being by Niven, Crit. Rev. Ther. Drug Carrier Sys, 12(2and3):151-231 (1995). One aspect covered in said review is the stability issue of protein formulations, aqueous solutions being less stable than powder formulation. So far, all powder formulations have been described as mainly amorphous.
A review of the permeation enhancers useful for the promotion of trans-mucosal absorption is found in Sayani et al., Crit. Rev. Ther. Drug Carrier Sys, 13(1and2): 85-184 (1996).
Patton et al., Inhale Therapeutic Systems, PCT WO 95/24183, claim a method for aerosolising a dose of insulin comprising providing the insulin as a dry powder dispersing an amount of the dry powder in a gas stream to form an aerosol capturing the aerosol in a chamber for subsequent inhalation.
It has been found that when insulin is combined with an appropriate absorption enhancer and is introduced into the lower respiratory tract in the form of a powder of appropriate particle size, it readily enters the systemic circulation by absorption through the layer of epithelial cells in the lower respiratory tract as described in U.S. Pat. No. 5,506,203. The manufacturing process described in said patent, comprising dissolution of insulin at acid pH followed by a pH adjustment to pH 7.4 and addition of sodium taurocholate before drying the solution by vacuum concentration, open drying, spray drying, or freeze drying, results in a powder composed of human insulin and absorption enhancer. The powder is characterized as mainly amorphous determined under a polarized light microscope. The desired particle size distribution is achieved by micronizing in a suitable mill, such as a jet mill, and the components may be mixed before or after micronizing. The biological effect of the powder obtained according to the methods described in this patent is only seen in the presence of a substantial amount of enhancer.
Platz et al., Inhale Therapeutic Systems, PCT WO 96/32149, describes spray drying of zinc insulin from a solution containing mannitol and a citrate buffer, pH 6.7. The inlet temperature is 120 to 122xc2x0 C., the outlet temperature 80-81xc2x0 C. The mass median aerodynamic diameter, MMAd, of the obtained insulin particles was determined to 1.3 to 1.5 xcexcm.
In his thesis, xe2x80x9cInsulin Crystalsxe2x80x9d, Munksgaard Publisher 1958, p. 54-55, Schlichtkrull describes crystallisation of zinc free, recrystallised porcine insulin from a solution comprising 0.01 M sodium acetate and 0.7%xcx9c0.12 M sodium chloride and 0.1% methylparahydroxybenzoate and using a pH of 7.0. The crystals obtained were 10-50 xcexcm rhombic dodecahedral crystals showing no birefringence.
Jackson, U.S. Pat. No. 3,719,655 describes a method of purification of crude porcine and bovine insulin by crystallisation. Zinc free crystals of insulin are obtained by crystallisation at pH 8.2 (range 7.2-10) in the presence of 0.5 M (range 0.2 M-1 M) of a sodium, potassium, lithium or ammonium salt. Crystallisation is achieved by addition of 1 N alkali metal hydroxide or 1 N ammonia to a solution of crude insulin in 0.5 N acetic acid to a pH of 8.2 is obtained. Alternatively, crystallisation is achieved in an aqueous solution of impure insulin at pH 8.2 by addition of solid sodium chloride to a concentration of sodium ions of 0.45 M. The crystals appear in the octadecahedral or dodecahedral forms, i.e. crystals belonging to the cubic crystal system.
Baker et al., Lilly, EP 0 709 395 A2 (filed Oct. 31, 1994) describe a zinc free crystallisation process for LysB28-ProB29 human insulin characterised by adjustment of the pH of a strongly buffered acid solution containing metal cations or ammonium ions and a preservative with metal hydroxide or ammonia to a value between 8.5 and 9.5.
The known methods for the manufacture of insulin particles of the desired size for pulmonary administration are cumbersome, generates problems with insulin dust and the investments in equipment are large. Furthermore, insulin is exposed to conditions where some denaturation is likely to take place. Thus WO 96/32149 discloses spray drying in a temperature range of 50xc2x0 C. to 100xc2x0 C., followed by milling of the particles to achieve to desired particle size.
Furthermore, the known powder formulations for pulmonary administration which have been described as mainly amorphous have a tendency to associate into aggregates in the dry powder.